(************************ LOCAL ATTRIBUTES ***************************)
  
PROCEDURE CollectLocalAttributes(
    READONLY t: Texture;
    periodic: BOOLEAN;
  ): REF ARRAY OF LocalAttributes.T;
  (*
    Computes the local invariants at every texel of "t",
    and returns them as a linear array.  
    
    If "periodic" is FALSE, ignores texels that are adjacent 
    to the border of the image (i..e, only considers texels
    with coordinates in "[1..NX-2]x[1..NY-2]").  This is 
    useful, for instance, if the texture "t" is a scanned image
    that is not actually periodic. *)

(************************ ENERGY ***************************)

PROCEDURE ComputeEnergy(
    VAR t: Texture;                    (* Current texture *)
    eval: LocalEvaluator;              (* The local energy function *)
    VAR (*OUT*) E: LONGREAL;           (* Energy of texture *)
    VAR (*OUT*) dEdt: RealPixelMatrix; (* Energy gradient *)
  );
  (*
    Computes the total energy "E" of a texture, and its gradient
    "dEdt" (the partial derivatives of "E" with respect to the texel
    components). *)